1. Field of the Invention
The present invention is directed to the field of package/container vacuum decay leak detection and more particularly to the testing of containers filled with either dry product or liquid product such as non-porous vials, ampoules, injection cartridges, ophthalmic product packages, syringes, pouches, blister packages and other packages containing critical medicinal and/or chemical products using a method of measuring vacuum decay within a test chamber in which a container being tested is sealed and wherein as a vacuum is being pulled within the test chamber the pressure levels are continuously monitored using an absolute pressure transducer, or both an absolute pressure transducer and a differential pressure transducer, such that pressure conditions within the test chamber over a period of time are used to indicate whether or not there is a leak in a container being tested. More specifically, the invention is directed to improvements maintaining an at rest vacuum condition in the testing system prior to tests being conducted.
2. Brief Description of the Related Art
There have been many innovation made with respect to the field of pressure testing of containers, packages and container and package seals. In the area of dry content package or container testing, the packages or containers are placed into a test cavity and subject to a change in surrounding pressure. In the field of vacuum package testing, a reduced pressure is established at least along an isolated portion of a package or package seal to determine if there are leaks in the packaging which are detected by monitoring the surrounding pressure to determine if any increase in pressure is detected that will reflect a leak in a seal or in a wall of the package or container under test. In some such tests, diaphragms or other covering devices may be used to seal any porous portion of a package under test or to prevent movement or destruction of a portion of the package or container under test. Some examples of such testing systems and methods are disclosed in U.S. Pat. No. 6,050,133 to Achter el al, U.S. Pat. No. 6,513,366 to Stauffer, U.S. Pat. No. 5,513,516 to Stauffer, U.S. Pat. No. 5,199,296 to Lehmann, U.S. Pat. No. 5,239,859 to Lehmann, U.S. Pat. No. 5,513,516 to Lehmann and U.S. Pat. No. 5,575,265 to Lehmann.
When testing packages and containers which include any liquid, care must be taken to account for vaporization of liquid from within a container which may give rise to false pressure readings at low vacuum pressures, During testing, the vaporizing liquid can increase the pressure in the test chamber such that drops in head space pressure caused by gas leakage cannot be accurately detected. To overcome this, vacuum testing procedures have been developed to account for the vaporization of liquids in containers under test. In some procedures, vacuum levels are drop to a level to vaporize the liquid content of a container after which the withdrawn vapor is effectively removed by freezing of the vapor. Some examples include U.S. Pat. No. 4,320,653 to Bernhardt and U.S. Pat. No. 4,409,817 to Edwards, Jr.
In U.S. Pat. No. 2,784,373 to Lawrance et al, a method and device for testing for leaks in containers that may contain a liquid are disclosed wherein a test chamber in which the container is placed is evacuated to pressures well below the vapor pressure of the liquid until a predetermined vacuum pressure is achieved, afterwhich, the test chamber is isolated from the source of vacuum and a pressure differential test is conduct between a start time and an ending time to determine any increases in pressure that may be caused by vaporized gases passing through small holes in the container, and thus provide an indication that the container has a leak. Other examples of testing systems that operate below the vaporization pressure of a liquid are disclosed in U.S. Pat. No. 4,426,876 to Kakumoto and a series of US patents to Lehmann, including U.S. Pat. Nos. 5,907,093, 6,082,184, 6,202,477, and 6,305,215.